Mix is a regular Elixir script that will use the Elixir on your PATH. You can do bin/elixir bin/mix help format.
josevalim
Creator of Elixir
AstonJ
cleaver
There’s a plugin for Atom which is an easy way to play around with this…
I was able to install 1.6 from master in a separate directory and point the plugin to that version while I work on 1.5
riverrun
I ran the new formatter on all of the libraries I maintain, and I think it’s a testament to the Elixir devs that 1) I was so confident that there would be no problems, and 2) it did work perfectly.
It was also funny to see what I thought was a concise two-line function call converted into a 14-liner 
josevalim
Creator of Elixir
riverrun
This is the example I was talking about. It’s from this example Phoenix app.
This wonderfully concise little function:
def remove_old_sessions(session_age) do
now = System.system_time(:second)
Enum.map(list_users(), &change(&1, sessions: :maps.filter(fn _, time ->
time + session_age > now end, &1.sessions)) |> Repo.update)
end
became this:
def remove_old_sessions(session_age) do
now = System.system_time(:second)
Enum.map(
list_users(),
&(change(
&1,
sessions:
:maps.filter(
fn _, time ->
time + session_age > now
end,
&1.sessions
)
)
|> Repo.update())
)
end
Ok, perhaps it’s a little easier to read now 
josevalim
Creator of Elixir
To be very honest, I think both before and after are not readable. The code is too dense. When you skip variables, you lose the opportunity to give names to values, so the reader needs to keep a lot in their head.
Here is one alternative:
def remove_old_sessions(session_age) do
now = System.system_time(:second)
for user <- list_users() do
new_sessions =
user.sessions
|> Enum.filter(fn {_, time} -> time + session_age > now)
|> Enum.into(%{})
user
|> change(sessions: new_sessions)
|> Repo.update()
end
end
Although it probably wouldn’t hurt to break it into more functions.
PS: if you want to further abuse comprehensions:
new_sessions =
for {_, time} <- user.sessions,
into: %{},
do: time + session_age > now
riverrun
net
For the last comprehension I think you mean
new_sessions =
for {key, time} <- user.sessions,
time + session_age > now,
into: %{},
do: {key, time}
josevalim
Creator of Elixir